Theoretical Study Of Teeth Internal Structure Detection And Early Caries Evaluation By Using Laser Ultrasound Technology

Clinical testing of teeth internal structure and clinical diagnosis of early caries have always been the research hotspot and difficulty in stomatology field. Compared with the existing clinical diagnosis techniques, laser ultrasonic technique has many advantages, such as non-contact, no stimulation, fast detection speed and so on. It has enormous development potential and limitless application in clinical detection field. The present thesis studies the detection of teeth internal structure and the quantitative diagnosis of early caries by using laser ultrasonics. The feasibility of laser ultrasonics using for dental clinical detection is analyzed. And provide a specific method for detection and diagnosis.The geometric model of the molar and incisor is achieved through the CT scan and the technology of 3D-reconstruction. On the basis of wave equation and thermoelasticity theory, a finite element model is accordingly developed to simulate ultrasound waves generated by a pulsed laser in human teeth.A new methods is proposed to detect teeth internal structure using longitudinal wave generated by laser ultrasonic technique. Longitudinal wave reflected in the interface of enamel and dentin, and it carried the information about enamel thickness. Through the study of the propagation characteristics of reflected longitudinal wave, we designed a detection method to get molar internal structure, compared the test results with the actual internal structure, the feasibility of the method has been verified.A new methods is proposed to evaluate early caries in quantitative detection using Rayleigh wave generated by laser ultrasonic technique. As the speed of Rayleigh wave is sensitive to the elastic modulus of the teeth surface, we evaluated the position, the demineralization degree and the 2D morphology of the caries region by solving the velocity field of Rayleigh wave on teeth surface. Through the 2D-FFT method and signal comparison, we evaluated the depth of the caries region.In this paper, the study results will provide theoretical basis for teeth internal structure and the evaluate of early caries by using laser ultrasound, and will help for the further development and application of laser ultrasonic technology in clinical testing.